Most bacteria of the genus Bacillus produce small polypeptides with potent antibiotic activity; yet, despite their medical importance, the biological function of these peptides and the mechanisms that control their formation are not at all understood. Recently, however, studies in this and other laboratories have suggested not only that the production of peptide antibiotics is linked to sporulation, but also that these substances play an essential role in the sporulation process. It is the purpose of the proposed research to elucidate the regulatory mechanisms that direct the transition from vegetative growth to sporulation in Bacillus brevis and related species and to define the function of peptide antibiotics in this process of differentiation. The proposed research will involve: (a) studies of the effect of the peptide antibiotic gramicidin on the specificity of transcription by purified RNA polymerase, (b) studies on the synthesis and degradation of RNA in vegetative and sporulating cells of B. brevis made permeable to small molecules by treatment with toluene, and (c) studies on sporulation and RNA synthesis in mutants of B. brevis that have lost the ability to synthesize peptide antibiotics or with an altered RNA polymerase.